Hot top lining



J. O. EDSTROM HOT TOP LINING July 9, 1968 Filed Nov. 2. 1965 Fig United States Patent 3,391,725 HOT TOP LENING John Olof Edstriim, Sandviken, Sweden, assignor to Sandvikens Jernverks Aktiebolag, Sandviken, Sweden, a Swedish corporation Filed Nov. 2, 1965, Ser. No. 505,049 Claims priority, application Sweden, Nov. 3, 1964, 13,240/64 6 Claims. (Cl. 164-449) ABSTRACT OF THE DISCLQSURE A hot top lining for a casting mold is nonhomogeneous in composition, being constituted by two (or more) integral layers-each containing fine grained refractory material and a binder-bonded together. Each layer is per se homogeneous. The layer immediately adjacent the cast metal contains refractory material having a smaller average gain size and with a higher heat resistance than that of the refractory material contained in the layer adjacent the casting mold.

The present invention pertains to hot tops or parts thereof for ingot molds or other casting molds, for instance hot top slabs with a very high insulating ability, low bulk density and high strength, the cross section of which is formed with at least two layers bonded to each other by means of a binder and containing refractory and organic material. The hot top can be made as a hood in one piece or of a number of slabs which are interconnected by means of wedges.

It is previously known to manufacture hot tops from refractory and organic material. These hot tops have had a homogeneous composition containing besides fine grained refractory material such as quartz smaller quantities of organic binder and fihrous organic and inorganic material, and satisfactory results have been achieved with such hot tops. They have, however, had certain disadvantages. Thus the fine grained refractory material has as a rule all consisted of quartz, which forms a line quartz powder after the disintegration of the hot top after the casting, said powder being dangerous because of the risk of silicosis. It has been tried to substitute the fine grained quartz by other refractory materials, but they have been found expensive, which has resulted in a substantial increase of costs of the hot tops. At the same time no improvement of the heat insulation properties or other properties has been obtained.

The present invention eliminates the above mentioned as well as other disadvantages of the previous hot tops and makes possible an economic manufacture of hot tops having improved properties.

As mentioned the hot top or the parts of which it is composed has a cross section consisting of at least two layers bonded together by a binder and containing refractory and organic material. The invention is in the main characterized in that the main ingredient in both layers is fine grained refractory material, the inner layers situated adjacent the cast steel or metal having a greater tightness and a substantially lower average grain size of the refractory material than the outer layer. The outer layer should at the same time have such a grain distribution that it is penetrable by arising gases. This can be attained by choosing a rather narrow screening interval.

Besides fine grained refractory material with different average grain size both layers contain a binder, which as a rule consists of organic material, preferably a resin or a synthetic resin glue and amounting to 1-l0% by weight of the composition. Normally the content of binder Patented July 9, 1968 is 3-8% and can be in the main similar for both layers or smaller in the inner layer than in the outer layer. The layers usually also contain up to 10% by weight of an organic, preferably fibrous material, for instance paper or paper pulp and up to 10% by weight of a refractory fibrous material, for instance asbestos, rock wool or glass wool. The content of organic fibrous material is often chosen within the range 17%, for instance about 3-4%, while the content of inorganic fibrous material suitably amounts to at the most 4%, for instance about l-2%. Also these contents can be in the main similar in both layers or lower in the inner layer than in the outer layer.

The hot tops according to the invention have a high heat insulation, the heat conduction between and 1000 C. being about 0.1 kcal./mh. C., and they also have a high mechanical strength even in thin sections and are therefore usually manufactured with thicknesses of 12-30 mm. The inner layer, which has a substantially lower average grain size than the outer layer and which should be very tight and highly refractory, is made very thin in comparison with the outer layer. The cross section should not be more than about 4-5 mm. thick and is as a rule from one to a few millimeters. The inner layer serves at the same time since it has an insulating function, to withstand the high temperature from the cast steel or metal and to resist adhesion to the sink head during the freezing of the casting. It is therefore important that the fine grained refractory material in this layer consists of highly refractory minerals or products which for instance consist of or contain silicates such as olivine and nephelite syenite, A1 0 or compounds containing A1 0 Z10 or compounds of ZrO quartz and/or compounds of alkalies, e.g. sodium, potassium and calcium. In order to obtain the tight structure which is desired in this layer the said refractory material should be very fine grained and should suitably have at least partly a powder consistency. At the same time the contents of binder and fibrous organic and inorganic materials should be relatively low in order to avoid undesirable gas development from this layer. The said fibrous material increase the cohesion and the insulation. The content of fibrous organic material can thus be l-5%, for instance about 34% and the content of fibrous inorganic material 0.53%, the latter content preferably not exceeding about 1-2%.

The outer layer, the cross section of which is substantially thicker than the inner layer, should in the first place have a high insulation, at the same time being refractory and having a high strength, so that it provides a reliable support for the thin inner layer.

In order to achieve the desired high heat insulation the fine grained refractory material in the outer layer can wholly or partly consist of slag or similar material or can at least partly consist of infusorial earth (Kieselguhr) or similar material. As the outer layer can be permitted to be less refractory than the inner layer it is possible to use common, easily available and cheap material in the outer layer such as compounds of alkalies and/or certain silicates, preferably unburned limestone and/or dolomite or sand. These materials give the outer layer the desired high insulating properties and a sufiicient mechanical strength as supporting layer. The outer layer being thick in relation to the inner layer the quantity of cheap materials therein is large in comparison with the quantity of highly refractory and more expensive materials in the inner layer, which brings down the total cost of materials for the hot top.

Closer details of the invention appear from the following specification with the darwings which show:

FIG. 1, a perspective view of the upper end of an ingot mold in which is mounted a hot top according to the invention.

FIG. 2, a part of a cross section on the line 22 in FIG. 1 of a hot top slab according to the invention.

In the ingot mold in FIG. 1 there is mounted a hot top comprising four slabs 11, 12, 13 and 14 which are held against the walls of the mold by wedges 15, 16, 17 and 18. It is also possible to make the hot top in one piece, for instance as a hood or to make it in parts shaped in some other suitable way. FIG. 2 shows a cross section of the hot top slab 11 in FIG. 1 with the thin inner layer 19 containing fine grained, highly refractory material and the outer thicker layer 20, having a fine grained refractory material with a substantially larger average grain size than in the inner layer. The other slabs 12, 13 and 14 are formed with layers, i.e. laminated in the same way. It is possible but not necessary to laminate also the corner wedges. The laminated hot tops or slabs for hot tops should be made as a unit with the layers firmly interconnected.

As mentioned the inner as well as the outer layer should contain both refractory and organic material. Both layers should, as main ingredient, contain fine grained refractory material, the inner layer adjacent the cast steel or metal having a substantially smaller average grain size than the outer layer, the latter suitably having a rather narrow screening interval. The grain sizes for the inner layer can suitably be chosen in such a way that more than 50% passes a screen of 0.105 mm. (140 mesh according to ASTM standard) and a substantial part, for instance more than or even more than also passes a 0.053 mm. screen (270 mesh). The grain sizes for the outer layer can be distributed in such a way that more than passes a 0.84 mm. screen (20 mesh) and more than preferably more than remain on a 0.053 mm. screen (270 mesh).

The organic material in the layers consists of the binder, which as a rule is organic, and/or some other organic material, preferably with a fibrous structure. The binder is suitably a resin glue as a synthetic resin, and the organic fibrous material is suitably paper, paper pulp or some other kind of plant fibres. The contents of binder and other organic, preferably fibrous material, can be in the main equal in both layers and should be relatively low, for instance 26%, for the binder and 27% for the other organic material. It has, however, been found as suitable in many cases to use a lower content or organic material in the inner layer than in the outer layer. It is for instance possible to have .24% organic fibrous material in the inner layer, and 37% in the outer layer. Also the binder content can suitably be lower in the inner layer than in the outer layer, for instance 24% and 46% respectively. Furthermore one of the layers or both layers can contain a fibrous refractory material as asbestos, rock wool or glass wool. The content of such material is as a rule up to 10%, preferably up to 5% and can suitably be lower in the inner layer than in the outer layer. In certain cases there is no such material at all, at least not in the inner layer. The content of fibrous refractory material is suitably 0.52% for both layers. The content of fibrous refractory material in the inner layer can be about 1% lower than in the outer layer, for instance 0.5-1%.

In the foregoing description, unless otherwise indicated, all percentages are by weight.

As mentioned the fine grained refractory material in the inner layer should comprise highly refractory and very fine grained minerals or products which can be crushed so that they are partly of powder consistency. They can consist of or contain quartz, silicates as olivine and certain syenites, A1 0 Zr0 and/ or refractory compounds of alkalies.

The fine grained refractory material in the outer layer can consist of compounds of alkalies and/or dolomite or sand. It can also wholly or partly consist of porous umterial as slag, int'usorial earth (kieselguhr) or the like. Certain slags from e.g. the metallurgical industry as well as limestone and/ or dolomite have been found useful in this connection. The slags have as expected good heat insulation properties in the same way as limestone and dolomite, which have a substantially lower heat conduction ability than for instance quartz. If the latter materials do not have too small grain sizes and have the actual narrow grain size distribution specified above there is surprisingly no disturbing gas development by disintegration of the carbonates which otherwise would disturb the function of the hot top. The gases which arises pass between the grains out of the layer. In order to conduct such gases away t e outside of the outer layer can be provided with grooves or channels, for instance arranged vertically, or there can be a number of recesses or holes in the layer having openings towards the outside, possibly in connection with grooves or channels of the said kind.

The following is an example of a laminated hot top slab according to the invention:

The slab consisted of two interconnected layers, the inner, thinner of which contained 87.594.5% fine grained olivine, partly as a powder, 36% synthetic resin glue, 26% paper or paper pulp and 0.51.5% asbestos or rock wool, the outer, thicker layer consisting of 84.593.5% finely crushed limestone with a rather even grain size, 36% synthetic resin glue, 37% paper or paper pulp and 05-25% asbestos or rock wool.

In the foregoing example the outer layer contains 70% of refractory material having a grain size between 0.84 and 0.053 mm. and the inner layer has 70% of refractory material having a grain size less than 0.105 mm. and 30% less than 0.05 3 mm. According to another example the fine grained refractory material in the inner layer consisted of crushed brick of a neutral or basic type, for instance in the main consisting of A1 0 or of burned dolomite, the outer layer containing a porous metallurgical slag. In the foregoing example the particles sizes of the refractory materials are within the ranges given above.

Besides the ingredients mentioned in the foregoing the outer layer can contain a minor quantity of exothermic material, for instance containing aluminum, magnesium and/ or zirconium. It is also possible to cover the outside of the outer layer with an exothermic material. By the said addition to the composition or said surface cover the properties of the hot top are further improved. It is also possible to apply a layer of a material the structure of which expands by heating, preferably a mica such as vermiculite, on the outside of the outer layer or on a part of the outside, for instance the lower part which is adapted for a tight contact with the ingot mold. In this way the contact between the hot top and the ingot mold can be improved, thereby effectively preventing formation of fins and similar on the ingot.

The invention is of course not confined to hot tops or parts of hot tops composed of two layers but comprises also hot tops consisting of three or more layers, the contents in adjacent layers varying as described in the foregoing.

In the foregoing description the word powder refers to material having a particles size less than 0.053 and preferably less than 0.025 mm.

I claim:

1. Hot top lining or part thereof for a casting rnold having a high insulating ability, low bulk density and high strength, the hot top being built up by a fine grained refractory material as a main constituent which is bonded together by a binder, said hot top comprising two different integral layers, an inner layer adjacent the cast metal and an outer layer adjacent the casting mold, said inner layer being thinner and containing a refractory material with a higher heat resistance and a smaller average grain size than said outer layer.

2. Hot top or part thereof according to claim 1 in which both layers besides fine grained refractory material, having smaller and greater average grain sizes respectively,

contains 110% of organic binder, up to 10% of organic 6. Hot top or part thereof according to claim 1 in which fibrous material and up to 10% refractory fibrous material. the outer layer is provided with external recesses.

3. Hot top or part thereof according to claim 1 in which the fine grained refractory material in the inner layer is Refeiwces Ciied at least partly of power consistency. 5 UNITED STATES PATENTS 4. Hot top or part thereof according to claim 1 in which 3 039 158 6/1962 Mueller X the fine grained refractory materlal 1n the outer layer com- 3,072,981 1/1963 Davidson X prises a porous material selected from the group consisting of slag, diatomaceous earth and kieselguhr. FOREIGN PATENTS 5. Hot top or part thereof according to claim 1 in which in 993,699 9 5 Great Britain the fine grained material in the outer layer is selected & from the group consisting of unburned limestone, dolomite SPENCER OVERHOLSER lmmy Ewmme' and sand. E. MAR, Assistant Examiner. 

